Three ways to save Earth from disaster

By Robert Matthews, Science Correspondent

12:01AM BST 28 Jul 2002

It is a space race with more at stake than superpower prestige. British scientists are at the forefront of efforts to deflect objects on a collision course with Earth after the revelation that an asteroid might strike our planet on February 1, 2019.

Proposals for ways of protecting the Earth from Near Earth Objects (NEOs) are being prepared for a conference sponsored by Nasa, the US space agency, in Washington DC in September.

While popular attention has centred on using nuclear missiles to blow up incoming NEOs - the solution used in Armageddon, the Hollywood film starring Bruce Willis - scientists now fear that such an approach would actually create thousands of smaller asteroids all still heading for Earth.

Instead, a number of methods of nudging asteroids off-course are being examined, including attaching either a rocket engine or a "solar sail" to their surface and pushing them away from our orbit.

American scientists last year held talks with Nasa about the possibility of using a nuclear engine attached to an incoming asteroid to deflect it. The engine would be flown to the asteroid on a conventional rocket: it would then land and fix itself to the object's surface. Firing the engine would push the asteroid far enough off its path to miss Earth.

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"It is like pushing a beach ball across a swimming pool using your nose," said one scientist present at the talks.

Dr William J Merline, a senior research scientist at the Southwest Research Institute in Boulder, Colorado, said: "We believe the most useful technique is that of using rocket propulsion. A nuclear weapon is probably not the best solution to deflecting an incoming asteroid. The use of rocket propulsion would require significant lead time before impact, but in the most probable scenario we would have sufficient time."

Another option being considered is to attach a "solar sail" to an asteroid rather than an engine. The sail would also be flown to the asteroid on a conventional rocket and embedded into its surface. Once in place, it would capture photons - particles of light emitted by the Sun - which would drive it just as a conventional sail on a boat is driven by wind, thereby nudging the asteroid off course.

Other scientists, however, argue that a more dramatic intervention is required. Dr Duncan Steel, an expert on asteroids at Salford University, said: "A rocket motor could just end up burying itself. There's little doubt that we would have to use a nuclear weapon."

According to Dr Steel, a nuclear explosion some distance from the NEO would unleash a shock wave of radiation that would vaporise material from the surface, gently moving the object off course.

The race for solutions to asteroid collisions was given fresh impetus last week when astronomers revealed that they had detected an asteroid, code-named 2002 NT7, which may strike the Earth on February 1, 2019. Measuring about 1 mile across and travelling towards the Earth at more than 60,000 mph, it would strike with the violence of a million H-bombs.

Astronomers are now carrying out further observations to plot the precise trajectory of 2002 NT7. While scientists believe that these will show that it will miss the Earth, they also insist that it is only a matter of time before a catastrophic impact does take place.

The Telegraph can reveal that earlier this month, officials from the Pentagon's Defence Advanced Research Projects Agency visited the University of Surrey, whose scientists are world leaders in microsatellite technology, to discuss the possibility of creating a defensive shield in space.

The microsatellites, which are cheap and easy to launch, could form a network of "watchdogs" stationed in deep space to give early warning of possible NEOs. Equipped with an optical telescope, each microsatellite would be capable of spotting NEOs, which are notoriously small and dark, and alerting ground-based observatories.

Microsatellites could also be used to land on an incoming NEO and investigate its mass, size and composition. Such information will be crucial to deflecting any object heading for Earth, say researchers.

"One thing we surely need to do is learn what asteroids are like, so that we could effectively interact with one if we needed to," said Clark Chapman, a scientist at the Southwest Research Institute. "We just don't know enough about asteroid surfaces and interiors to understand whether we could bolt something onto it, dig into it, or affect it from above its surface."